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Bureau of Mines Information Circular/1983 




A Guide to Geologic Features 
in Coal Mines in the Northern 
Appalachian Coal Basin 

By Paul W. Jeran and Jacqueline H. Jansky 




UNITED STATES DEPARTMENT OF THE INTERIOR 



: r." "t 



Information Circular 8918 
•1 



A Guide to Geologic Features 
in Coal Mines in the Northern 
Appalachian Coal Basin 

By Paul W. Jeran and Jacqueline H. Jansky 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



This publication has been cataloged as follows: 




V 



!^ 



<j 






Jeran, P. Vi 

A guide to geologic features ia coal mines in the northern Appa- 
lachian Coal Basin, 

(Information circular ; 8918) 

Bibliography: p. 16. 

Supt.ofDocs.no.: 128.27: 8918. 

1. Coal mines and mining— Appalachian Region— Safety measures. 
2. Coal— Geology— Appalachian Region. 3. Ground control (Mining). 
I. Jansky, Jacqueline H. II. Title. III. Series: Infomiation circu- 
lar (United States. Bureau of Mines) ; 8918. 

-^f^m&^^\H 622s [622.8] 82-600359 



'1 CONTENTS 

-0 



V 



Page 



Abs t ract 1 

Introduction. 2 

Orientation 2 

Llthology 4 

Sands tones 4 

Shales 4 

Limes tones 6 

Bedding 6 

Sedimentary features 7 

Structural features 10 

Clay veins and mud-filled fractures 15 

Summary 16 

Bibliography 16 

ILLUSTRATIONS 

1. Diagram illustrating strike and dip 3 

2. Orientation aid 3 

3. Illustration of orientation aid use 3 

4 . Wet bedding plane 5 

5 . Normal bedding 6 

6 . Crossbedding 6 

7 . Sandstone channel cutting out coalbed 8 

8. Sandstone channel with coal layers terminating against sandstone 8 

9. Sandstone channel with coal layers deformed next to sandstone 8 

10. Supported kettlebottom 8 

11. Kettlebottom with surrounding roof rock sloughed 9 

12. Void left by fallen kettlebottom 9 

13. Anticline and syncline 11 

14. Mud-filled fractures in roof 11 

15. Joints in roof rock 12 

16. Slickenside showing polishing and grooving 12 

17. Slickenside showing curved surface. 13 

13. Slickenside showing planar surface 13 

19. Faults 14 

20. Faults recorded on a section map 14 

21. Clay vein 15 

22. Mud-filled fracture transecting coalbed 15 



LIST OF UNIT 


OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


cm 


centimeter m meter 


in 


inch pet percent 


ft 


foot 



A GUIDE TO GEOLOGIC FEATURES IN COAL MINES IN THE NORTHERN 

APPALACHIAN COAL BASIN 

By Paul W, Jeran and Jacqueline H, Jansky 



ABSTRACT 

This Bureau of Mines report has been prepared to provide a means 
whereby mineworkers without specific geologic training can recognize and 
record the existence of potentially hazardous geologic features en- 
countered in coal mines. Each geologic feature described in this report 
has been implicated in roof failure. Through the recording of the ob- 
servations of mineworkers, based on this report, a geologic map of mine 
workings and the associated ground control problems can be compiled. 
From such maps, the trends of changes and features can be determined and 
projected ahead of mining. The face crew can be alerted to a potential 
problem and what to look for as the face is advanced. 





'Geologist/ Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 



INTRODUCTION 



Roof falls are a major cause of death 
and injury to underground coal miners. 
Aside from the human tragedy, many days 
of nonproductive work are used to clean 
up and resupport fallen roof. The Bureau 
of Mines, through its ground control re- 
search program, is analyzing the roof 
fall problem and developing techniques 
that will reduce the number and severity 
of accidents due to ground failure. 

Areas of bad roof are local occurrences 
in the majority of coal mines. The dif- 
ference between good and bad roof can 
usually be attributed to a change in the 
roof strata, provided that the mining 
method or technique has not been changed. 
Geologic evidence for this change is usu- 
ally present but goes unnoticed until the 
situation becomes critical and sometimes 
is not noticed even then. 

This report has been prepared to 
acquaint the readers with potentially 
hazardous geologic features that they can 
readily observe and record. Each of the 
features described in this report has 
been implicated in roof failures; how- 
ever, no feature or change in roof strata 
guarantees that roof control problems 



will or will not occur. With time and 
experience, a geologic map of a mine's 
workings and the associated ground con- 
trol problems can be compiled. From such 
maps, the trends of changes and features 
can be determined and projected ahead of 
mining. The face crew can be alerted to 
a potential problem and what to look for 
as the face is advanced. 

This report describes a method of de- 
termining the orientation of planar fea- 
tures. It has sections on general rock 
description (lithology), features devel- 
oped during deposition of strata (sedi- 
mentary features), and features that 
result from the rocks being deformed by 
geologic forces (structural features). 

Illustrations are used to provide vis- 
ual examples of each feature. The black 
and white stick used in the photo- 
graphs (all from mines in the northern 
Appalachian Coal Basin) is a reference 
scale to give the viewer an idea of the 
size of each feature. The alternating 
bands on the stick are 6 in (15.2 cm) 
long, and the entire stick is 30 in 
(0.76 m) long. 



ORIENTATION 



Most geologic features occur in groups, 
i.e., where one is observed others may be 
expected. For this reason, it is impor- 
tant to record each occurrence of each 
feature on a suitable scale mine map. 
With planar features, such as bedding, 
clay veins, slips, and joints, the ori- 
entation of each is important, 

A geologist records the attitude or 
orientation of any plane by two values — 
strike and dip (fig. 1). Strike is the 
direction with respect to some reference 
(usually north) of a horizontal line in 
the plane. In a flat-lying coal mine 
(grades less than 10 pet), the intersec- 
tion of the plane and the roof is usually 
a reasonable approximation of a horizon- 
tal line. In figure 1 the strike is a° 
to the right of the reference direction 



(inby entries). The dip is the angle 
measured in the vertical plane perpen- 
dicular to the strike downward from the 
horizontal plane to the feature plane. 
In figure 1 the dip is b° downward to the 
right of the strike. 

The symbol used to denote strike and 
dip on a map is shown in figure 1. The 
long line is drawn parallel to the strike 
direction with respect to the reference 
direction. The short line indicates the 
dip direction and has the dip angle 
written next to it. Figure 1 shows the 
map symbol for the illustrated strike and 
dip. 

Geologists usually use magnetic com- 
passes with clinometers to measure ori- 
entation. These are readily available 




FIGURE 1. = Diagram illustrating strike and dip. 

for under $100 each, and with a little 
training almost anyone can use one. How- 
ever, as an alternative, a simple orien- 
tation aid card (fig. 2) method is sug- 
gested for use underground. 

The reference direction chosen is inby 
parallel with the entries. To determine 
the strike of a planar feature, the card 
user stands facing inby with the trace of 
the planar feature overhead. The orien- 
tation aid card is held flat in the hand 
and the arrow is oriented so that it 
points inby parallel to the entries at 
the location of the measurement. By 
using the upper half of the aid (labeled 
strike), the direction of the trace 
of the feature in the roof is estimated 
relative to the reference direction 
(fig. 3). The number of degrees left or 
right (strike direction) is recorded. 

To estimate the dip, the card user 
faces, in the same direction as the 
strike, the trace of the feature plane in 
the rib (fig. 3). The orientation aid 




° 80 90 80 

FIGURE 2, - Orientation aid. 




Read dip 
{card vertical) 



y 



/ -Trace of plane 
/ in floor 



FIGURE 3. - Illustration of orientation aid use. 



card is held vertically, and the left or 
right edge is aligned with the trace 
of the plane in the rib. A weighted 
string is held at the center of the dia- 
gram and is allowed to fall within the 
lower arc on the card (labeled dip). The 
number of degrees and their relationship 
(right or left) to the strike are 
recorded. 



These data should be transcribed to the 
mine section map later. Maps with these 
data should be kept, not discarded, 
when the section is mined out. Con- 
sultation of these maps when mining in 
the vicinity of old workings will alert 
the crew to the features and orientations 
they may encounter as they advance the 
face. 



LITHOLOGY 



Within the coal mining industry there 
are many terms used to describe the rocks 
encountered in mining. While these terms 
have meaning within a given mine or min- 
ing area, this meaning can vary from one 
mine or area to another. This can lead 
to confusion and misunderstanding when 
the experience gained from one area is 
related to a mine in another area. Ge- 
ologists use a rock classification system 
that describes rocks precisely. This 
system is too complex for general use. 
This section has been included to provide 
the readers with a basic rock classifica- 
tion that is compatible with the geologic 
classification, 

Lithology is the description of rocks 
based on color, mineralogic composition, 
and grain size. In U.S. coalfields, the 
rocks associated with bituminous coalbeds 
generally fall into one of the three 
types of sedimentary rocks — sandstone, 
shale, or limestone. Sedimentary rocks 
are (1) the result of weathering and ero- 
sion of the preexisting rock, (2) the 
product of deposited organic material, or 
(3) the chemicals left when seawater 
evaporates. Thus sedimentary rocks can 
be classified as fragmental, biological, 
or chemical. The following is a brief 
coimnentary on distinguishing each of the 
three sedimentary rock types. 



SANDSTONES 

Sandstones are fragmental sedimentary 
rocks made of visible sand-sized grains 
cemented together by a filler materi- 
al. Sandstones are sandy to the touch 
(like sandpaper). The color of sand- 
stone ranges from a gray to red to tan. 



Sandstones can be identified by the visi- 
ble sand grains. 

Occasionally sandstones contain the 
mineral mica. This mineral looks like 
small flakes of shiny cellophane. Where 
mica is lying on a bedding plane, the 
bedding plane will appear shiny and the 
sandstone will tend to separate along 
this layer. Where observed, this should 
be noted as micaceous sandstone. From a 
distance, e.g., when looking at the top 
of a high roof fall from its base, a 
mica-covered bedding plane may appear as 
shiny as a slickenside but will not have 
the grooves or scratches. A close in- 
spection of the rock should determine if 
the shiny surface is a micaceous bedding 
plane or a slickenside. 

SHALES 

Shales are also fragmental sedimentary 
rocks, but the grains are so small that 
no individual grains can be seen by the 
naked eye. These rocks are formed by the 
compaction of mud. Shales tend to break 
into layers and feel smooth to the touch. 
Usual colors are gray or black but can be 
tan, red, or green. Shales may be iden- 
tified by their very fine grains, smooth- 
ness, ease with which they can be 
scratched by a piece of steel, and a 
tendency to break into flat pieces. When 
a piece of shale is scratched, the re- 
sulting powder is the same color as the 
rock itself. Shales associated with 
coalbeds may contain the imprint of fos- 
sil leaves. Bedding planes in shale can 
be highly reflective when wet (fig. 4). 
Wet bedding planes should not be mistaken 
for slickensides. 




FIGURE 4. - Wet bedding plane. 



LIMESTONES 

Limestones are sedimentary rocks that 
can be fragmental, biological, and/or 
chemical. Limestones are made of the 
mineral calcite, which generally exists 
as small grains. They are generally mas- 
sive rocks, may contain seashell fossils, 
and rarely break into flat slabs as does 
shale. Limestones are generally gray 
to tan in color, but when scratched, 
the resulting powder is light gray to 
white. Note that this is different from 
shale, which produces powder essentially 
the same color as the rock itself. 

BEDDING 

Any description of a roof problem 
should give at least the rock type(s) 
involved and their thickness. The 



individual layers making up the rock 
stratum are called bedding, and where 
this can be observed, the bedding thick- 
ness should be noted as well as the 
thickness of the rock type. There are 
two types of bedding that may be observed 
and noted. First is normal bedding 
(fig. 5) , where the bedding parallels 
the coalbed. Second is crossbedding 
(fig. 6), where the bedding is other than 
parallel with the coalbed. 

Categorization of a rock layer as 
crossbedding should be done carefully. 
To be considered crossbedding, all the 
bedding must be inclined to the coalbed. 
If only one or two surfaces are inclined 
and the balance of the bedding is paral- 
lel to the coalbed, a group of slicken- 
sided surfaces has been encountered, not 
bedding. 







FIGURE 5. - Normal bedding. 



Complex 
crossbedding 

Normal bedding-^j^^^ 

Simple 
crossbedding - 

Normal bedding 




FIGURE 6. - Crossbedding. 



Geologists use the term "fades change" might be expected. Where observed, this 



to describe the lateral change of rock 
types. When the immediate and/or main 
roof rock changes types within a distance 
of 200 ft (61 ra) or less, then problems 



should be noted on the mine map. Roof 

bolting machine operators can be very 

helpful by noting, during drilling, where 
and when such changes occur. 



SEDIMENTARY FEATURES 



the usual 

miners are 

out," or 

thinned by 



One particular rock feature is the 
sandstone channel. This feature may 
affect only the roof, or may partially or 
wholly cut out the coalbed. Where the 
coalbed has been cut out, 
descriptive terms used by 
"want," "wash out," "pinch 
"fault," Where the coal is 
rock protruding from the roof, the fea- 
ture is commonly called a "roll" or 
"pinch out." Where these can be traced 
to a sandstone bed or channel, they 
should be called a sandstone channel. 
Since "fault" Is a specific structural 
feature, this term should never be 
applied to a sandstone channel. Details 
to be noted on a mine map are (1) the 
trend of the sandstone channel, (2) the 
width of the feature measured at the top 



of the coalbed, and (3) the 
coal remaining in place. 



thickness of 



Sandstone channels can be observed in 
two distinct occurrences. First is the 
true cutout where the individual layers 
of coal are cut by the sandstone 
(figs. 7-8). Note that the layers of 
coal terminate at the sandstone and there 
is little change in coal thickness as 
mining approaches the channel. The 
second occurrence is where the sandstone 
has been pushed into the coalbed, causing 
the coal to be squeezed out to either 



side of the sandstone channel (fig. 9). 
The layers of coal are bent downward, 
which may show some wrinkling, and the 
coalbed may double in thickness on either 
or both sides of the sandstone. Slicken- 
sided surfaces are common. 

Another lithologic feature is the ket- 
tlebottom. This feature is also called 
"caldron bottom," "pot bottom," or "coal 
pipe," It is the mud cast of a fossil 
trunk or root of a tree or fern, which 
extends upward into the roof rock above a 
coalbed. It is commonly surrounded by a 
thin layer of coal and/or slickensides. 
This feature may fall at any time without 
warning. Where kettlebottoms are com- 
monly found, roof control plans contain 
specific methods of supporting or taking 
them down. Figure 10 shows a supported 
kettlebottom in place. Figure 11 shows a 
kettlebottom with the rock around it hav- 
ing sloughed off; the shape of the bark 
of the original tree can be seen. Fig- 
ure 12 shows the void left by a kettle- 
bottom that has fallen. 



Kettlebottoms are usually found 
groups. The location and diameter 



m 
of 

each kettlebottom should be noted on the 
mine map. If a kettlebottom has fallen 
out, the thickness of the fallen piece 
should also be recorded. 



^■;^!;-: Sandstone" 
■^r'.rv- channel ". 

I Width of channel] 
I measured at top 
of coalbed I 



TTTT- 




No coal below channel 
\ 




FIGURE 7. - Sandstone channel cutting out 
coalbed. 




FIGURE 8. - Sandstone channel with coal lay- 
ers terminating against sandstone. 




.Sandstone channel-.'. 

/ / / / / y y / x2^ '•'•■: '•''-''■' '■■'■ '■■'''/\, - 
fCoalbed_ ' ^^ ' ■■"■■■■' '-■■ ■''- ' ^^ 



Normal 
coalbed 



iBedding.Width of channel I Thicken- 

bent measured at top jng of 

I down I °^ coolbed coalbed 



_Coalbed disturbed by_ 
sandstone channel 



Normal 
coalbed 



30 in of coal below channel 



Coalbed 9 ft thick 
this side of channel 



r'>-;"i:o/ 6/ Slip, 9 in-offset, dips 
-i'lv;^;/ r 30° toward U 



FIGURE 9. - Sandstone channel with coal lay- 
ers deformed next to sandstone. 



H 


gps. ^ 




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FIGURE 10. - Supported kettlebottom. 




FIGURE n. - Kettlebottom with surrounding roof rock sloughed. 







FIGURE 12. " Void left by fallen kettlebottom. 



10 



STRUCTURAL FEATURES 



When sufficient stresses are applied to 
rock strata, the strata will either bend 
or break. Where rock strata are bent, 
geologists use the term fold. Folds are 
usually described as either anticlines, 
where the beds form an arch, or syn- 
clines , where the beds form a trough 
(fig. 13). Occasionally, minor folds may 
be observed in the working place. These 
usually result from the local movement of 
the coal or associated rocks past each 
other. The major folds found in coal 
basins are generally so broad that an 
entire mine would lie within only a small 
portion of one. 

Breaks in the rock strata are easily 
observed. The geologist uses the general 
term "fracture" to describe all breaks or 
cracks. All fractures should be noted, 
particularly their orientation, length, 
and the distance between fractures having 
the same or similar orientations. Some- 
times the fractures have deposits in 
them, and this should be noted (fig. 14). 

There are several types of fractures 
that have been given specific names be- 
cause of their shape. The most common of 
these is the joint. Joints are reason- 
ably straight and smooth cracks in rock 
along which there has been no movement. 
Soft-coal miners are generally familiar 
with cleat in coal. Cleat in coal is the 
same as joint in rock. Where a crack or 
group of cracks that look like coal cleat 
is found in the roof or floor rock, the 
term "joint" is used to describe them. 
Figure 15 shows joints in roof rocks; 
some material is in place, and some is 
partially fallen. 

Generally speaking, the cleats and 
joints within a mine are consistent in 
orientation or spacing. To verify this, 
they should be measured at intervals 
[about every 500 ft (152 m) ] . Should any 
change be found in either orientation or 
spacing, it should be noted and recorded 
on the mine map. Experience has shown 
that such changes are indicators of local 
geologic disturbance and potential mining 
problems . 



Where there has been movement of the 
rock or coal along a fracture, the result 
may be a slickensided surface. Movement 
of less than 1 in (2.54 cm) can create a 
slickensided surface. These surfaces are 
generally polished with either scratches 
or grooves all in one direction 
(fig. 16). Small slickensided surfaces 
are usually curved (fig. 17), while 
larger ones tend to be fairly planar 
(fig. 18). The orientation of these sur- 
faces should be measured and also the 
direction of last movement. The direc- 
tion of last movement can be determined 
by rubbing the surface in the same direc- 
tion as the grooves or scratches. One 
direction will feel smoother than the 
other. This smoother direction is the 
direction in which the missing block of 
rock last moved relative to the rock sur- 
face being rubbed. 

For practical purposes, three terms may 
be used to describe a fracture where 
the rocks and/or coal have moved — slick- 
enside, slip, and fault. Slickenside 
should be used where a slickensided sur- 
face is observed but the amount of move- 
ment cannot be determined. Slip should 
be used where the feature is confined to 
three or fewer entries. Fault should be 
used where the feature can be traced 
across a section or several entries. In 
general, slips will exhibit smaller move- 
ment than faults. 

The description of a slip should in- 
clude its orientation, the direction of 
last movement, the amount of offset, and 
the length it can be traced across the 
mine workings. If only a small portion 
[about 1 ft2 (0.29 m^)] of slip is ob- 
served, then it would be better to call 
this a slickenside. 

The description of faults is more com- 
plex. The orientation of the fault and 
the direction and amount of movement must 
be measured and recorded. Faults may 
occur with one or more planes of movement 
and with relative movements in opposite 
directions. Where more than one plane of 
movement is present, the proper term is 



11 





Anticline Syncline 

FIGURE 13. - Anticline and syncline. 




FIGURE 14. - Mud-filled fractures in roof, sometimes called hill slips. 



12 




FIGURE 15, - Joints in roof rock. 




FIGURE 16. - Slickenside showing polishing and grooving. 



13 




FIGURE 17. - Slickenside showing curved surface. 




FIGURE 18. = Slickenside showing planar surface^ 



14 



fault zone (fig. 19). The width of the 
fault zone should be measured and its 
orientation estimated. The offset of the 
strata on either side of the zone should 
be measured or estimated. 

Faults may dip at any angle from per- 
pendicular to parallel to bedding. At 
the two extremes it is necessary to re- 
cord direction of last movement or the 
direction of the scratches or grooves in 
the slickensided surfaces of the fault 
planes. 

Larger faults may not exhibit slicken- 
sides but may have a zone of ground mate- 
rial in them. This material comes from 
the rocks and coals adjacent to the fault 
that were crushed when the movement took 



place along the fault. If present, this 
material should be noted and its thick- 
ness measured and recorded. 

When recording faults on the mine map, 
solid lines should be used only where the 
fault crosses entries and has been ob- 
served. Dotted or dashed lines can be 
used where it crosses pillars or barri- 
ers. Except for faults that parallel the 
bedding, all faults have one side that is 
higher than the other. This should be 
noted on the mine map by placing a U (for 
up side) on the side of the fault that is 
higher or a D (for down side) on the side 
of the fault that is lower. The dip of 
the fault plane can then be recorded as 
toward the high or low side. 




^^ ^ A- Fault zone 



\A 



^\ 




^^. xSlip plane 






" ^^(^'^'■f^''^:'^'-^^'^-'''''"^^^^^^^''^'^'^'^-'^^ 




/'Cloy vein 



yV^. ' ^jr'.■■V.^kV■- ' jy■^^ j ^i^>^!yj:'^^^ 



mifim 



^Him^MM 






Offset — 



^ Fault zone 
crushed material 



FIGURE 19. - Faults. 



nn/pnnnnnnnc 

nmnnnnnnnc 

njnnnnnnnnc 

DcJannnnnnnnE 



■\ 



fZone is 20 to 40 ft wide 
Fault Offset is 4 ft 

< Dips 65° toward u 




Slip offset is Iff, dips 45° toward 5 



nDDnnnnc 
nnnnnnE 
nnnnnDL 

DDDDDE 

Vf Off set ranges from 
^ ,j I ft in entry I to 
FaultiRft in entry 5 



Clay vein~N 
in roof • 



/Clay vein 
V in floor 



w ■ • III ciiii J ^ 
Dips 40° toward D 




nnnnnnnc 

nnnnnnnc 

nnnnnnc 

DDDDDE 

Horizontal fault is 2 ft above 
bottom, crushed zone is 4 in 
thick. Clay vein shows offset 

FIGURE 20. - Faults recorded on section mop. 
Note faults rarely are perfectly straight. 



15 



The fault sketches in figure 19 are ex- 
posures in the outside rib of entry No. 1 
of figure 20, which illustrates each of 



these faults as they might be recorded on 
a map of the section. 



CLAY VEINS AND MUD-FILLED FRACTURES 



Clay veins and mud-filled fractures 
are found in several of the northern 
Appalachian coalbeds. Increased methane 
emissions and water 
reported when these 
penetrated by mining. 
tures penetrate the coalbed from above, 
unstable roof commonly occurs. Miners 



inflows have been 

features are first 

Where these fea- 




usually call any rock-filled fracture a 
"clay vein" or "spar." These two fea- 
tures differ markedly in shape and should 
be recorded separately. The clay vein 
(fig. 21) is typically "Christmas tree" 
shaped with the coal-rock contact being 
interf ingered. The mud-filled fracture 
(fig. 22) is usually planar with the 
coal-rock contact relatively smooth. 
Where the two features occur together, 
they should be measured and recorded 
separately. 

To describe either feature, its orien- 
tation and thickness should be measured. 
The length of penetration into the coal- 
bed should be noted [for example, clay 
vein from roof 36 in (0.9 m) into 48-in 
(1.2-m) thick coalbed, strike 30° right, 
dip 80° left, tapers from 12 in (0.3 m) 
wide at roof line to zero] . 




FIGURE 21. = Clay vein. 



FIGURE 22, = Mud-filled fracture transecting 
coalbed. 



16 



SUMMARY 



This report has been prepared to give a 
nongeologist a means of recognizing, 
describing, and recording potentially 
hazardous geologic features commonly en- 
countered in underground coal mining. 
The major geologic features present in 
coal mines in the northern Appalachian 
Coal Basin that may pose ground control 
hazards during mining are illustrated. 
The report cannot possibly cover all geo- 
logic features. If the user finds a fea- 
ture that is not covered in this report, 
he or she should describe and record what 
is seen in as simple words as possible. 
Very often a simple sketch with the 
written description can be very helpful 
in conveying to others what was observed. 

Most mines have encountered one or more 
of the illustrated features and have, 
with varying degrees of success, mined 
through them. No records are usually 



kept when changes have been made in min- 
ing method and/or roof support to cope 
with such hazards. Then when similar 
problems are encountered several years 
later, the whole process of finding a 
solution must be repeated. 

If remedial methods are recorded along 
with the geologic features on mine maps, 
then, over the course of a mine's life, 
these maps may be consulted as similar 
features are encountered, and what did 
not work in the past can be avoided. As 
sufficient data are gathered, the mining 
method and roof support can be tailored 
to meet specific local conditions, there- 
by saving both time and money while 
safely and efficiently mining the coal. 
In addition, the use of standard ter- 
minology will allow the transfer of min- 
ing experience from one area to another 
with respect to specific features. 



BIBLIOGRAPHY 



1. Bates, R. L. , and J. A. Jackson. 
Glossary of Geology, 2d ed. 1980, 
749 pp. 

2. Cox, R. M. Why Some Bolted Mine 
Roofs Fail. Trans. AIME, v. 256, 1974, 
pp. 167-171. 

3. Headlee, A. J. W. Fracture Zones 
in Mine Strata. Min. Cong. J., v. 30, 
No. 4, April 1944, pp. 57-60. 



Geological Survey, 4th Ser, Inf. Circ. 
75, 1974, 17 pp. 

6. Lahee, F. H. Field Geology. 
McGraw-Hill Book Co., Inc., New York, 
5th ed., 1952, 883 pp. 

7. McCabe, K. W. , and W. Pascoe. 
Sandstone Channels: Their Influence on 
Roof Control in Coal Mines. MSHA IR 
1096, 1978, 24 pp. 



4. Kearns, E. G. , Jr. Clay Dikes in 
the Pittsburgh Coal of Southwestern 
Greene County, Pennsylvania. M.S. The- 
sis, WV Univ., Morgantown, WV, 1970, 
50 pp. 

5. Kent, B. H. Geologic Causes and 
Possible Prevention of Roof Fall in Room- 
and-Pillar Coal Mines. Pennsylvania 



8. Stahl, R. L. Guide to Geologic 
Features Affecting Coal Mine Roof. MSHA 
IR 1101, 1979, 18 pp. 

9. Thrush, Paul W. (comp. and ed. by). 
A Dictionary of Mining, Mineral, and Re- 
lated Terms. BuMines SP 2-68, 1968, 
1269 pp. 



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